traits.hpp

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#ifndef JOIN_CORE_TRAITS_HPP
#define JOIN_CORE_TRAITS_HPP
 
// C++.
#include <type_traits>
#include <utility>
 
namespace join
{
    template <typename... Ts>
    struct overload;
 
    template <>
    struct overload<>
    {
        void operator() () const;
    };
 
    template <typename First, typename... Ts>
    struct overload<First, Ts...> : overload<Ts...>
    {
        using overload<Ts...>::operator();
 
        std::type_identity<First> operator() (First) const;
    };
 
    template <typename... Ts>
    struct overload<void, Ts...> : overload<Ts...>
    {
        using overload<Ts...>::operator();
 
        std::type_identity<void> operator() () const;
    };
 
    template <typename T, typename... Ts>
    using match_t = typename std::invoke_result_t<overload<Ts...>, T>::type;
 
    template <typename T, typename... Ts>
    inline constexpr std::size_t find_index_v = 0;
 
    template <typename T, typename First, typename... Ts>
    inline constexpr std::size_t find_index_v<T, First, Ts...> =
        std::is_same_v<T, First> ? 0 : find_index_v<T, Ts...> + 1;
 
    template <typename T, typename... Ts>
    inline constexpr std::size_t count_v = (std::size_t{0} + ... + std::is_same_v<T, Ts>);
 
    template <typename T, typename... Ts>
    inline constexpr bool is_unique_v = count_v<T, Ts...> == 1;
}
 
#endif